Controversial official assessments of the possible cost of Brexit should never have been kept secret, the head of the Government’s budget watchdog has suggested.

Robert Chote, the chairman of the Office for Budget Responsibility, said that “in an ideal world”, ministers would have planned to publish them all along.

The papers, drawn up by civil servants in David Davis’s Department for Exiting the EU, suggested that Brexit will leave Britain worse-off under any likely scenario – with growth depressed by 5% over the next 15 years if the UK gets a comprehensive trade agreement or 8% if it leaves without a deal.

Their leak to the Buzzfeed website sparked fury among Conservative Brexiteers, with the chair of the pro-Brexit European Research Group of Tory MPs Jacob Rees-Mogg describing their findings as “highly speculative”.

Prime Minister Theresa May said the analysis was incomplete and had not been signed off by ministers.

But ministers were forced into agreeing to release the documents after coming under parliamentary pressure from Labour and critics on the Tory benches.

Speaking to the Institute for Government, Mr Chote admitted that it had “not been a happy period”.

“I think it’s fair to say that there’s clearly a logical case for having a good study done of the economic impact of the different models or the different potential outcomes that the Government is thinking of looking at,” he said.

“And I think there’s also a case for saying that in the current environment… if you do a lot of that work and you circulate it around government it’s not entirely surprising that it leaks and gets into the public domain.

“In an ideal world, you would have embarked on this exercise in the hope and expectation that you end up with a published project or outcome that can be shared with the public in general as well as within government.”